Formula
Percentage amount = base x percent / 100. Part-of-whole percent = part / whole x 100. Percentage change = (new value - original value) / |original value| x 100.
Percent Calculator
Percent-of, percentage change, increases and decreases on one dedicated calculator page.
Worked example
For 25% of 200, calculate 200 x 25 / 100 = 50. If 160 increases to 200, the percentage change is (200 - 160) / 160 x 100 = 25%.
Professional note
Master’s Tip: always name the base. “25%” by itself is incomplete until the page says 25% of what, compared with what, or changed from what.
Regional and unit assumptions
Standard or basis: percent as parts per hundred. This is arithmetic only and does not apply tax, payroll, grading, discount or finance rules by itself.
Assumptions and limitations
- A percent-of calculation needs a base number.
- A part-of-whole calculation needs a non-zero whole value.
- Ordinary percentage change is undefined when the original value is zero.
- Negative values and decreases should be interpreted with the visible formula, not just the sign.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Percentage amount = base x percent / 100. Part-of-whole percent = part / whole x 100. Percentage change = (new value - original value) / |original value| x 100.
Standard or basis
Standard or basis: percent as parts per hundred. This is arithmetic only and does not apply tax, payroll, grading, discount or finance rules by itself.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: always name the base. “25%” by itself is incomplete until the page says 25% of what, compared with what, or changed from what.
Related calculators
Questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the base number.
How do I find what percent one value is of another?
Divide the part by the whole, then multiply by 100. The whole must not be zero.
How do I calculate percentage change?
Subtract the original value from the new value, divide by the original value, then multiply by 100.
Why do percentage mistakes happen so often?
Because the base or denominator is hidden. Two percentages can look similar while answering different questions.
Calculation note
Percentage arithmetic is compact, but that compactness hides the base. A good percentage page keeps the denominator visible.